This invention is a circuit for the high speed generation of a cursor in a high resolution gray scale display, and more specifically comprises a set of video RAM's having a capacity larger than that needed for the storage of the display, the added capacity being used to store a duplicate band of video containing the cursor. The high speed internal video transfer capability of the RAM being used to create this band as needed.
Modern reprographic systems require sophisticated displays. In particular, such a system may have a high-resolution gray scale display. However, in such a system the generation and accurate tracking by the display cursor generated by a mouse or other cursor generating device requires additional circuitry or processing overhead.
In a typical system, a memory would be used to store the image of the display, and the cursor would be masked into the memory at the appropriate position. Then, as the cursor generating device such as a mouse is moved, the cursor would have to be deleted from its original position, and re-generated in its new position. Since the color of the cursor is uniform and fixed, such as black, the creation of the new cursor is relatively simple. However, at the same time, the position of the previous cursor must be returned to its original gray scale color, and that requires that the original image gray levels must be stored in another memory of some kind. When the cursor is moved to a new position, the new cursor must be generated and the gray levels of the previous position must be determined from the memory and masked into the display. Since there are a plurality of bits per pixel, these masking and storing steps may proceed at an undesireably slow speed. What is required is a system which can accomplish these steps at high speed and preferably without the requirement of added circuitry.